.container:before,  .container:after {
  content: "";
  display: table;
}

.container:after {
  clear: both;
}

.item {
  float: left;
  margin-bottom: 15px;
}
.first-item {
  clear: both;
}

.last-row, .last-row ~ .item {
  margin-bottom: 0;
}